On-screen displays have been used with image display systems, such as television receivers, to give a viewer information concerning the operation of the system. One example of a use for such on-screen displays is to display operating parameters of the system, such as the channel number to which the television receiver is tuned or a graphical representation of the sound volume level in the form of a bar graph. Such displays are generally used while the viewer is changing the associated parameter. Thus, when the viewer is changing the channel, the channel number is displayed superimposed atop the received main image, and when the viewer is changing the sound volume, the volume level bar graph is similarly displayed.
Another example of a use for such on-screen displays is in sleep timers. Sleep timers have been developed to enable a viewer to select a time when the receiver should automatically turn itself off should the viewer fall asleep, or otherwise lose interest in watching. The viewer sets the turn-off time through the use of the remote control. During the last minute or two before the receiver is to turn off, current sleep timers gradually turn down the sound volume so that a sudden change in the sound level will not awaken a sleeping viewer. In addition, current sleep timers provide an on-screen display, superimposed atop the main image, to visually indicate to the viewer that the receiver will be turning off in a short period of time. During this time interval, sleep timers are responsive to some action by a viewer, such as receipt of a signal from a remote control, to restore the volume and display of the television receiver to their normal functions. If no action is taken by a viewer during this pre-turn-off time period, then at the selected turn-off time, power is removed from the television receiver.
One on-screen display used by known sleep timers includes a textual message on the display screen indicating the amount of time (e.g. number of seconds) before the television receiver is going to turn itself off. Other on-screen displays include an iconic symbol, which may include simple animation, for example, a bar graph with a bar that gradually grows in length from one end of the on-screen display toward the other. When the bar reaches the other end of the on-screen display, the time period is over, and the receiver turns itself off. Other on-screen displays produce a black border from one or more edges of the screen. This border gradually increases in width, obscuring more and more of the image. When the border completely covers the screen, the time period is over, and the receiver turns itself off.